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Abstract:

Electric motors and generators, in which a non-contact ultrasonic
suspension of the rotor of the electric motor, are provided. The
non-contact ultrasonic suspension is achieved by the formation of an
elevated-pressure gaseous microfilm between conjugated surfaces of
saddle-resonators and trunnions of a bearing system.

Claims:

1. An electric motor or generator, comprising: a housing, a rotor, and a
stator rigidly attached to the housing; a first piezoelectric element
rigidly attached to the housing; a first saddle having a concave surface
and rigidly attached to the first piezoelectric element; a first trunnion
rigidly attached to the rotor, the first trunnion having a concave
surface that is a conjugate of the concave surface of the first saddle
and is spaced apart from the concave surface of the first saddle by a
gap; and wherein the first piezoelectric element, the first saddle and
the first trunnion form a bearing system configured to suspend the rotor
for rotation in relation to the stator.

2. The electric motor or generator of claim 1, wherein: the first
piezoelectric element is operative to undergo oscillatory deformation
when subjected to an electric potential; and the first saddle is
operative to undergo oscillatory deformation in response to the
oscillatory deformation of the first piezoelectric element, wherein the
first saddle is configured to generate with the oscillatory deformation a
first field of acoustical energy in a gaseous medium located within the
gap between the concave surfaces of the first saddle and the first
trunnion.

3. The electric motor or generator of claim 1, wherein a natural
frequency of a zero-order mode of umbrella oscillation of the first
saddle substantially coincides with a natural frequency of a zero-order
radial mode of oscillation of the first piezoelectric element.

4. The electric motor or generator of claim 1, further comprising a
generator operative to excite the first piezoelectric element.

5. The electric motor or generator of claim 4, wherein the generator is
operative to excite the first piezoelectric element at a frequency
corresponding to a zero-order mode of umbrella oscillation of the first
saddle.

6. The electric motor or generator of claim 4, wherein the generator is
operative to excite the first piezoelectric element at a natural
zero-order radial mode of oscillation.

7. The electric motor or generator of claim 1, wherein the first saddle
has a Q factor of approximately 1,000 to approximately 10,000.

8. The electric motor or generator of claim 1, wherein an axial play
between the first saddle and the first trunnion is approximately 1 μm
to approximately 40 μm.

9. The electric motor or generator of claim 1, wherein the concave
surface of the first saddle is spaced apart from the concave surface of
the first trunnion by a gap of approximately 0.5 μm to approximately
20 μm.

10. The electric motor or generator of claim 2, wherein: the first saddle
is configured to direct the field of acoustical energy toward a center of
curvature of the concave surface of the first trunnion and to shape the
field of acoustical energy as a spherical wave; the concave surface of
the first trunnion is operative to reflect the wave so that a standing
acoustical wave is formed in a gap between the concave surface of the
first trunnion and the concave surface of the first saddle; and wherein
the first trunnion and the first saddle are configured to generate
radiation acoustic pressure resulting from the standing wave and acting
on the concave surface of the first trunnion and the concave surface of
the first saddle, and to suspend the rotor at least in part for rotation
in relation to the stator when the standing wave is present.

11. The electric motor or generator of claim 1, wherein the first saddle
and the first trunnion comprise glass.

12. The electric motor or generator of claim 2, further comprising: a
second saddle having a concave surface and being rigidly attached to the
first piezoelectric element so that the second saddle is operative to
undergo oscillatory deformation in response to the oscillatory
deformation of the second piezoelectric element; and a second trunnion
rigidly attached to the rotor and having a concave surface that
substantially matches in size and shape the concave surface of the second
saddle and is spaced apart from the concave surface of the second saddle
by a gap, wherein the second saddle is configured to generate with the
oscillatory deformation a second field of acoustical energy in a gaseous
medium located within the gap between the concave surfaces of the second
saddle and the second trunnion.

13. The electric motor or generator of claim 12, wherein: the first and
second saddles are rigidly attached to respective first and second
substantially planar surfaces of the first piezoelectric element so that
the first piezoelectric element is located intermediate the first and
second saddles, the first and second surfaces of the first piezoelectric
element extending in a direction substantially perpendicular to an axis
of rotation of the rotor; the first piezoelectric element is polarized in
a direction substantially perpendicular to the first and second surfaces
of the first piezoelectric element; and the second saddle is located
intermediate the first saddle and the rotor.

14. The electric motor or generator of claim 12, wherein: substantially
cylindrical outer surfaces of the first and second saddles are rigidly
attached to a substantially cylindrical inner surface of the first
piezoelectric element; the first piezoelectric element is radially
polarized; and the second saddle is located intermediate the first saddle
and the rotor.

15. The electric motor or generator of claim 2, further comprising: a
second piezoelectric element rigidly attached to the housing and
operative to undergo oscillatory deformation when subjected to an
electric potential; a second saddle having a concave surface and being
rigidly attached to the second piezoelectric element so that the second
saddle is operative to undergo oscillatory deformation in response to the
oscillatory deformation of the second piezoelectric element; and a second
trunnion rigidly attached to the rotor and having a concave surface that
substantially matches in size and shape the concave surface of the second
saddle and is spaced apart from the concave surface of the second saddle
by a gap, wherein the second saddle is configured to generate with the
oscillatory deformation a second field of acoustical energy in a gaseous
medium located within the gap between the concave surfaces of the second
saddle and the second trunnion.

16. The electric motor or generator of claim 15, wherein: the first
saddle is rigidly attached to a substantially planar surface of the first
piezoelectric element that extends substantially perpendicular to a
direction of rotation of the rotor; the second saddle is rigidly attached
a substantially planar surface of the second piezoelectric element that
extends substantially perpendicular to a direction of rotation of the
rotor; the first piezoelectric element is polarized in a direction
substantially perpendicular to the substantially planar surface of the
piezoelectric element; and the second piezoelectric element is polarized
in a direction substantially perpendicular to the substantially planar
surface of the second piezoelectric element.

17. The electric motor or generator of claim 16, wherein the first
piezoelectric element is positioned intermediate the rotor and the first
saddle, and the second piezoelectric element is positioned intermediate
the rotor and the second saddle.

18. The electric motor or generator of claim 16, wherein the first saddle
is positioned intermediate the rotor and the first piezoelectric element,
and the second saddle is positioned intermediate the rotor and the second
piezoelectric element.

19. The electric motor or generator of claim 15, wherein: a substantially
cylindrical outer surface of the first saddle is rigidly attached to a
substantially cylindrical inner surface of the first piezoelectric
element; a substantially cylindrical outer surface of the second saddle
is rigidly attached to a substantially cylindrical inner surface of the
second piezoelectric element; and the first and second piezoelectric
elements are radially polarized.

20. The electric motor or generator of claim 18, wherein the first saddle
is positioned intermediate the rotor and the first trunnion, and the
second saddle element is positioned intermediate the rotor and the second
trunnion.

21. The electric motor or generator of claim 18, wherein the first
trunnion is positioned intermediate the rotor and the first saddle, and
the second trunnion is positioned intermediate the rotor and the second
saddle.

22. A bearing system for suspending a rotating component in relation to a
non-rotating component, comprising: a first piezoelectric element rigidly
attached to the non-rotating component and operative to undergo
oscillatory deformation when subjected to an electric potential; a first
saddle having a concave surface and rigidly attached to the first
piezoelectric element, the first saddle operative to undergo oscillatory
deformation in response to the oscillatory deformation of the first
piezoelectric element, and the oscillatory deformation of the first
saddle configured to generate a first field of acoustical energy in a
gaseous medium adjacent to the concave surface; and a first trunnion
rigidly attached to the rotating component, the first trunnion having a
concave surface that is a conjugate of the concave surface of the first
saddle and spaced apart from the concave surface of the first saddle by
the gaseous medium, wherein the concave surface of the first trunnion is
configured to be subjected to the first field of acoustical energy in
response to the oscillatory deformation of the first saddle.

23. A method for suspending a rotating component in relation to a
non-rotating component, comprising: providing a bearing system comprising
a piezoelectric element rigidly attached to the non-rotating component; a
saddle having a concave surface and rigidly attached to the piezoelectric
element; and a trunnion rigidly attached to the rotating component, the
trunnion having a surface that is a conjugate of the surface of the
saddle and is spaced apart from the surface of the saddle by a gap; and
applying a voltage potential to the piezoelectric element sufficient to
excite the piezoelectric element so that the piezoelectric element
induces oscillatory deformation in the saddle, the oscillatory
deformation generating a field of acoustic energy in a gaseous medium
within the gap, the field of acoustic energy interacting with the
conjugate surfaces of the trunnion and the saddle to produce a standing
wave that supports the rotating component at least in part in relation to
the non-rotating component.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit under 35 U.S.C. §119(e) of
U.S. Provisional Application No. 61/378,703, filed Aug. 31, 2010, the
contents of which are incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Statement of Technical Field

[0003] The invention relates to the field of electric motors, generators,
and other devices having rotating components suspended from non-contact
bearings.

[0004] 2. Description Of Related Art

[0005] Brushless motors operating on direct or alternating current are
well known in the art. Such motors typically comprise a brushless
acceleration unit, which includes a stator and a rotor, and an axial
system. In the conventional synchronous or asynchronous brushless motors,
the stator windings generate a rotating electromagnetic field. The
rotating electromagnetic field interacts with the electromagnetic field
of the rotor windings or with the permanent magnet field of the rotor,
which creates a torque on the motor rotor. The rotor is installed on an
axis which is fixed by bearings. Usually these are plain or
rolling-element bearings.

[0006] Some brushless electric motors operate on the principle of
non-contact support. For example, various electrostatic, magnetic, and
superconducting contactless suspensions/supports have been suggested. See
for example, Maleev, P. I., New types of gyroscopes. Leningrad:
Sudostroenie, 1971, pages 9, 31. The operating principle of these devices
resides in creating forces of either electrostatic or magnetic repulsion
between a saddle-resonator and a corresponding trunnion.

[0007] A shortcoming of motors incorporating various electrostatic,
magnetic, and superconducting contactless suspensions/supports is the
significant technological difficulty involved in their implementation.
This has contributed to relatively poor technical specifications and
performance for motors of this type. For example, such motors tend to
have relatively low load-bearing capacity, produce adverse torques, and
involve complicated stabilization in space on account of considerable
gaps and so on. The technological difficulties associated with such
motors has also resulted in devices which have relatively high cost.
Accordingly, motors incorporating these principles have failed to find
broad application in commercial practice.

[0008] There are also known in the art various devices based on the
formation of three-axis contactless ultrasonic supports. Such devices are
discussed for example in Ukraine Patent No. 4169 to Petrenko, et al.
which concerns a design for a gas-bearing precision instruments, and in
USSR Patent No. 1782316 to Petrenko, et al. for a reliance precision
instrument. However, these references are generally limited to various
generic supports as opposed to motors arrangements.

[0009] Also known in the art are non-contact support systems that involve
a gas support or bearing employed in a gas-dynamic gyroscope. See, e.g.
Proceedings of the VII St-Petersburg International Conference on
Integrated Navigation Systems, St. Petersburg, 2000, pp. 106-110. These
systems are based on the idea of creating a gas micro-film of elevated
pressure between the adjoining or conjugate surfaces of the
saddle-resonator and of the trunnion. The elevated pressure area in this
method is created owing to the dynamic characteristics of the gas stream
formed in the gap between the adjoining surfaces of a gas turbine
(saddle)--trunnion assembly.

[0010] Among the disadvantages of the gas support systems are significant
technological complications related to the formation of a gas stream with
the required dynamic parameters. For example, the requisite gas stream
formation involves the complex configuration of the gap between the
adjoining surfaces, the turbine design, and the requirement for highly
stable turbine rotation. Other problems with the gas stream approach
include: the inability to use that method in static mode, such as when
the turbine/trunnion are immobile); the high energy demand (specifically
when the system goes from static condition to movement); the inadequate
three-axis stability of the support due to the considerable gap between
the adjoining surfaces (as large as 1 mm for some designs) and
fluctuation of the gas stream; significant gas-dynamic drag torques of
such supports (as high as 10-3 gcm); jerky motion; and the high cost
of such supports/bearings. Moreover, gas supported motors are known to be
difficult to stabilize, which in many cases requires significant and
careful rotor balancing, especially when working at high rotation speeds.
Specifically, the rotors in such systems need to be well balanced to
avoid "beating" effect, which is characterized by jerky movement of the
axis of rotation in various directions during the rotation. This happens
when the center of mass does not coincide with the axis of rotation.

SUMMARY OF THE INVENTION

[0011] The inventive concepts relate to economical motors and generators
each with a fixed axis that uses ultrasound contactless support. Electric
motors and generators with improved technical characteristics, namely
decreased moment of friction force and power consumption, increased
specific weight carrying ability, and increased spatial stability of the
rotational axis, are provided.

[0012] The electric motor disclosed herein includes a rotor mounted on an
axle. Upper and lower spherical trunnions are centered relative to the
axle and attached to the axle. Each of the trunnions respectively engage
a similar spherical (concave) surface formed from corresponding upper and
lower annular saddles or saddle-resonators. The saddle-resonators and the
trunnions are arranged such that there is only a minimal amount of axial
play between the conjugated surfaces of the saddle-resonator and
trunnion. For example, the axial play between the saddle-resonator and
the trunnion can be within 1 to 40 μm. The saddle-resonators are
centered with respect to the trunnions and are attached to a
piezoelement. The piezoelement is secured within a motor housing which
can also support the stator of the motor. The piezoelement is
electrically connected to an excitation generator.

[0013] In the first three embodiments of the electric motor which shall be
hereinafter described, the piezoelement is includes a planar annular
piezoelement that is symmetrical with respect to the axle. The
piezoelement has opposing end surfaces to which electrodes are attached
for exciting the piezoelement. Further, the piezoelement is polarized in
a direction normal to the planar end surfaces that carry the electrodes

[0014] In a first embodiment of the electric motor, the annular
saddle-resonators are accommodated intermediate the trunnions, with the
piezoelement being arranged intermediate the saddle-resonators. In this
arrangement, the saddle-resonators engage the piezoelement along the
opposite planar end surfaces of the piezoelement.

[0015] The stator and rotor in the first embodiment of the electric motor
are arranged outside of the saddle-resonators and trunnions, with the
piezoelement being mounted on the housing along its outer cylindrical
surface. In this first embodiment, the housing is in the form of a
cylindrical sleeve, with the respective piezoelement and stator being
attached to the internal cylindrical surface of the housing.

[0016] In a second embodiment of the electric motor, the piezoelement is
in the form of a combination of two symmetrically arranged
piezoelements--the upper and lower ones, with the annular
saddle-resonators being rigidly attached to the respective piezoelements.

[0017] In this embodiment, the upper saddle-resonator contacts the
respective piezoelement along the upper end surface, and the lower
saddle-resonator contacts the respective piezoelement along the lower end
surface.

[0018] Further, the stator and the rotor are advantageously accommodated
intermediate the upper and lower piezoelements.

[0019] In a third embodiment of the electric motor the trunnions are
arranged intermediate the upper and lower saddle-resonators, with the
upper saddle-resonator engaging the upper piezoelement along the lower
planar end surface, and the lower saddle-resonator engaging the lower
piezoelement along the upper planar end surface of the respective
piezoelement, and the stator and rotor being accommodated intermediate
the trunnions.

[0020] In a fourth, fifth and sixth embodiment of the electric motor which
shall hereinafter be described, the piezoelement is in the form of an
annular cylinder symmetrical with respect to the axis and radially
polarized. The electrodes are applied onto the inner and outer
cylindrical surfaces of the piezoelement. In the fourth embodiment of the
electric motor, the annular saddle-resonators are accommodated
intermediate the trunnions and are mounted on the piezoelement so that
their cylindrical surfaces are attached to the inner cylindrical surface
of the piezoelement. In this embodiment the stator and rotor are
advantageously arranged outside of the saddle-resonators and trunnions.

[0021] In the fifth embodiment of the electric motor, the piezoelement is
in the form of a combination of two symmetrically arranged annular
cylinders--the upper and lower ones, with the annular saddle-resonators
being rigidly attached to the respective piezoelements.

[0022] The annular saddle-resonators are accommodated intermediate the
trunnions and mounted on the upper and lower cylindrical piezoelements.
The outer cylindrical surfaces of the annular saddle-resonators are
rigidly attached to the inner cylindrical surfaces of the respective
piezoelements. In this embodiment of the motor, the stator and rotor are
advantageously accommodated intermediate the upper and lower
saddle-resonators.

[0023] In a sixth embodiment of the electric motor, the trunnions are
accommodated intermediate the annular saddle-resonators. The
saddle-resonators are mounted on the upper and lower cylindrical
piezoelements so that their cylindrical surfaces are rigidly attached to
the inner cylindrical surfaces of the respective piezoelements.

[0024] The stator and rotor are advantageously arranged intermediate the
upper and lower trunnions.

[0025] In accordance with a further aspect of the inventive concepts
disclosed herein, embodiments of electric motors and generators include a
housing, a rotor, and a stator rigidly attached to the housing. The
embodiments also include a first piezoelectric element rigidly attached
to the housing, and a first saddle having a concave surface and rigidly
attached to the first piezoelectric element. The embodiments further
include a first trunnion rigidly attached to the rotor. The first
trunnion has a concave surface that is a conjugate of the concave surface
of the first saddle and is spaced apart from the concave surface of the
first saddle by a gap. The first piezoelectric element, the first saddle,
and the first trunnion form a bearing system configured to suspend the
rotor for rotation in relation to the stator.

[0026] In accordance with a further aspect of the inventive concepts
disclosed herein, embodiments of bearing systems for suspending a
rotating component in relation to a non-rotating component include a
first piezoelectric element rigidly attached to the non-rotating
component and operative to undergo oscillatory deformation when subjected
to an electric potential. The embodiments also include a first saddle
having a concave surface and rigidly attached to the first piezoelectric
element. The first saddle is operative to undergo oscillatory deformation
in response to the oscillatory deformation of the first piezoelectric
element, and the oscillatory deformation of the first saddle configured
to generate a first field of acoustical energy in a gaseous medium
adjacent to the concave surface. The embodiments further include a first
trunnion rigidly attached to the rotating component. The first trunnion
hays a concave surface that is a conjugate of the concave surface of the
first saddle, and is spaced apart from the concave surface of the first
saddle by the gaseous medium. The concave surface of the first trunnion
is configured to be subjected to the first field of acoustical energy in
response to the oscillatory deformation of the first saddle.

[0027] In accordance with a further aspect of the inventive concepts
disclosed herein, a method for suspending a rotating component in
relation to a non-rotating component includes providing a bearing system
comprising a piezoelectric element rigidly attached to the non-rotating
component; a saddle having a concave surface and rigidly attached to the
piezoelectric element; and a trunnion rigidly attached to the rotating
component. The trunnion has a surface that is a conjugate of the surface
of the saddle and is spaced apart from the surface of the saddle by a
gap. The method further includes applying a voltage potential to the
piezoelectric element sufficient to excite the piezoelectric element so
that the piezoelectric element induces oscillatory deformation in the
saddle, the oscillatory deformation generates a field of acoustic energy
in a gaseous medium within the gap, and the field of acoustic energy
interacts with the conjugate surfaces of the trunnion and the saddle to
produce a standing wave that supports the rotating component at least in
part in relation to the non-rotating component.

[0028] Those skilled in the art will appreciate that while the present
invention has been described in terms of a motor, the concepts and
arrangements described herein can also be used to form electric
generators. Accordingly, all such references to electric motors should
also be understood to include electric generators.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Embodiments will be described with reference to the following
drawing figures, in which like numerals represent like items throughout
the figures, and in which:

[0030] FIG. 1 is a cross-sectional view of a first embodiment of an
electric motor that is useful for understanding the inventive
arrangements.

[0031] FIG. 2 is a cross-sectional view of a second embodiment of an
electric motor that is useful for understanding the inventive
arrangements.

[0032] FIG. 3 is a cross-sectional view of a third embodiment of an
electric motor that is useful for understanding the inventive
arrangements.

[0033]FIG. 4 is a cross-sectional view of a fourth embodiment of an
electric motor that is useful for understanding the inventive
arrangements.

[0034] FIG. 5 is a cross-sectional view of a fifth embodiment of an
electric motor that is useful for understanding the inventive
arrangements.

[0035] FIG. 6 is a cross-sectional view of a sixth embodiment of an
electric motor that is useful for understanding the inventive
arrangements.

DETAILED DESCRIPTION

[0036] The invention is described with reference to the attached figures.
The figures are not drawn to scale and they are provided merely to
illustrate the instant invention. Several aspects of the invention are
described below with reference to example applications for illustration.
It should be understood that numerous specific details, relationships,
and methods are set forth to provide a full understanding of the
invention. One having ordinary skill in the relevant art, however, will
readily recognize that the invention can be practiced without one or more
of the specific details or with other methods. In other instances,
well-known structures or operation are not shown in detail to avoid
obscuring the invention.

[0037] The present invention concerns an electric motor in which a
non-contact ultrasonic suspension of the rotor of the electric motor is
provided. The non-contact ultrasonic suspension is achieved by the
formation of an elevated-pressure gaseous microfilm between conjugated
surfaces of a saddle-resonator and of a trunnion. Thus, the mechanical
contact between the motor elements is completely eliminated.
Consequently, friction is also substantially eliminated, except for
friction associated with air or any other gas, and an unlimited service
life can potentially be achieved. The elimination of mechanical contact
also yields high smoothness of running and, consequently, substantial
reduction of the level of rotational jerking motion. Damping of rotor
oscillation provided by the resilience of the elevated-pressure gaseous
microfilm provides a considerable decrease in the vibration and noise
levels associated with the motor. The gaseous microfilm also allows the
electric motor to accelerate to high speeds. Although the invention is
generally described in terms of an electric motor, those skilled in the
art will appreciate that it is not limited in this regard. For example,
the inventive arrangements can be applied similarly to electric
generators and other devices having rotating components suspended from
non-contact bearings.

[0038] In each embodiment of the invention described herein, the formation
of the ultrasonic contactless bearing support is achieved at each moment
of time by means of a standing acoustic wave formed in the gaseous layer
defined by the adjoining surfaces of the saddle-resonator and the
trunnion. The resulting acoustic radiation pressure between the adjoining
surfaces of the saddle-resonator and the trunnion is a function of the
thickness of the gap therebetween. In the various embodiments of the
invention, the gap is several microns to several dozens of microns, and
simple calculations show that nonlinear acoustic effects are at work.

[0039] The nonlinear perturbation of pressure (Langevin acoustic radiation
pressure), calculated at a given point on an ideal wall, is of the order
of the square of the Mach number and it is given by the equation (1):

P = ρ 0 v 0 2 / sin 2 ( ω c l 0 )
, ( 1 ) ##EQU00001##

Where P is point pressure on the surface of the resonator; [0040]
ρ0 is undisturbed gas density; [0041] ν0 is disturbance
velocity; [0042] c is the speed of sound in gas; [0043] l0 is the
length of the acoustic resonator (the gap thickness); [0044] ω is
the cyclic frequency of disturbance (ω=ν2π, where ν is
frequency of disturbance).

[0045] From the foregoing equation it will be appreciated that as the
value of l0→0 the value of P→∞. This anticipated
theoretical result has been found to correspond well to the experimental
results.

[0046] The force acting on each point of the resonator equals dF=PdS,
where dS is an element of the surface of the resonator (the conjugate or
adjoining surface of the trunnion). As long as there is a complete
symmetry of the acoustic resonator formed by the adjoining or conjugate
surfaces of the saddle-resonator and of the trunnion (which is true in
our case for the spherical resonator), the resulting vector F would be
always directed along the axis of symmetry and will be determined from
the relationship:

F = ∫ S P S = P ∫ S n S
, ( 2 ) ##EQU00002##

where n is the inner normal to the trunnion surface. Note that since F is
a vector, the integral on the right side of the equation (2) has to be a
vector too. It is a normal practice in physics to express dS as a product
of the n (normal vector to the surface at that point) and dS (the
elementary surface area). In this case the elementary surface area is the
inner surface of the trunnion.

[0047] Estimates show that with an excitation frequency of 104 to
105 Hz and excitation power of about 10° to 101 W, the
disturbance velocity created in the acoustic resonator owing to the
resonant vibration of the saddle-resonator will be about 10-1 . . .
100 m/s. Therefore, for the gap thickness of l0=30 μm,
frequency ν=20 kHz, support area S=5 cm2, disturbance velocity=1
m/s and at normal atmospheric pressure, the load-bearing capacity of the
bearing support would be about 0.15 kg(f), which corresponds well to the
experimental results. This load bearing capacity is calculated by using
formula (I) to calculate the generated pressure P and then calculating
the force F=P×S (S is the contact surface area between the trunnion
and the saddle). The experimentally established magnitude of the gap
thickness amounts to 0.5 to 20 μm which is equivalent to the initial
axial play of the system (the double gap thickness) of 1 to 40 μm. As
used herein, the term "axial play" refers to potential motion of the
axis/bearing assembly in space due to mechanical tolerances in the
bearing support. When axial play occurs, the axis is not aligned in one
direction but can instead vary in position and alignment to some extent.

[0048] The process of non-contact ultrasonic rotor suspension utilized for
the present invention is somewhat different from the ultrasonic
levitation effect. The effect of ultrasonic levitation in the 20 to 200
kHz range takes place with gaseous layer thicknesses of several to tens
of millimeters which is greater by over three orders of magnitudes than
in the technical solution disclosed herein. Examples of the effect of
ultrasonic levitation are described in Method and apparatus for acoustic
levitation--U.S. Pat. No. 5,036,944--Filed Mar. 24, 1986; Cylindrical
acoustic levitator/concentrator--U.S. Pat. No. 6,467,350--Filed Mar. 15,
2001; Levitated crystal resonator--U.S. Pat. No. 5,604,392--Filed May 12,
1995; Method for transferring levitated objects--U.S. Pat. No. 6,575,669
--Filed Oct. 17, 2001; Ultrasonic clutch--U.S. Pat. No. 6,964,327--Filed
Dec. 11, 2002.

[0049] Indeed, the significant wavelength λ for this ultrasonic
range in gas is 2=C/ν=1.5-15 mm, while the period of ultrasonic
levitation will be defined as λ/2. In contrast, in our invention,
effects of nonlinear acoustics of a higher order take place. This
underlies the high precision capabilities of the inventive embodiments
disclosed herein (axis stability in space with accuracy down to mere
micrometers), which could not be attained with ultrasonic levitation.

[0050] In the embodiments disclosed herein, the piezoelement has the
capacity of exciting therein longitudinal standing waves (radial mode of
annulus ring oscillation) and a set of natural frequencies νm
according to expression.

where [0051] EP--Young's modulus of the piezoelement material;
[0052] RP--middle radius of the piezoelement annulus; [0053]
ρp--specific weight of the piezoelement material.

[0054] The saddle-resonator is made with a capacity of exciting therein
transverse flexural waves (with the annulus oscillation mode identical to
"umbrella" vibrations) and a set of natural frequencies νn
according to the following expression:

[0055] where [0056] E--Young's modulus of the saddle-resonator material;
[0057] R--middle radius of the saddle-resonator annulus; [0058]
Ix--moment of inertia of the section with respect to axis; [0059]
IP--polar moment of inertia of the section; [0060]
ρ2--specific weight of the saddle-resonator material.

[0061] In the presented embodiments the conjugated surfaces of the
saddle-resonator and trunnion are shaped to form a gaseous acoustic
resonator. With such an arrangement, the angle of incidence of the
acoustic wave relative to the normal to the surface should be close to
zero, and the wave reflection coefficient should be close to unity.
Therefore, the saddle-resonator and the trunnion are made of an elastic
material to satisfy the condition of required wave impedance, namely:
ρ0cρ1c1; ρ0cρ2c2, where
ρ1c1,ρ2c2 are the density and velocity of
sound in the trunnion and saddle-resonator material, respectively;
ρ0c are the density and velocity of sound in the gas gap. These
conditions are satisfied by glass. Hence, the saddle-resonators and
trunnions are made of glass in the embodiments disclosed herein. The
invention is not limited in this regard, and other materials can also be
used provided that they satisfy the condition stated above with respect
to the required wave impedance. The experimentally established degree of
surface congruency and roughness of the conjugated surfaces on glass
satisfy the conditions of 1 μm and 0.1 μm, respectively.

[0062] Referring now to FIG. 1, there is shown a first embodiment of the
electric motor. The electric motor includes a rotor and a stator. The
rotor includes an axle 1, upper and lower spherical trunnions 2, 3, and a
rotor winding 8. The stator includes annular shaped upper and lower
saddles or saddle-resonators 4, 5, a stator winding 7, and a
piezoelectric element or piezoelement 9. The piezoelement 9 is excited by
an excitation generator 11. The axle 1, upper and lower spherical
trunnions 2, 3, upper and lower saddle-resonators 4, 5, stator 7, rotor
8, and piezoelement 9 can be contained within a motor housing 6 as shown.

[0063] The axle 1 is positioned symmetrically along a symmetry axis O-O
(which is also referred to herein as a motor axis) on which the spherical
upper trunnion 2 and lower trunnion 3 are centered and fastened. In this
context, centering implies alignment of the center of the sphere (as
defined by the curvature of the trunnion) with the axis of symmetry. The
upper and lower spherical trunnions 2, 3 have spherical (convex) surfaces
of substantially the same shape and dimensions as the spherical surfaces
defined by the respective upper 4 and lower 5 annular saddle-resonators.
The matching spherical surfaces of the upper trunnion 2 and the upper
saddle-resonator 4, and the matching spherical surfaces of the trunnion 3
and the saddle-resonator 5 are referred to herein as conjugate surfaces.

[0064] In the embodiment shown in FIG. 1, the upper and lower
saddle-resonators 4, 5 are situated intermediate the trunnions 2, 3. The
saddle-resonators 4,5 are centered in a similar way with respect to the
trunnions 2,3 (in respect to the axle 1) and are secured to the annular
piezoelement 9 at the opposite end surfaces. The piezoelement 9 is
polarized normally to the planar end surfaces, i.e. the polarization
vector F is perpendicular to the end surfaces, and the electrodes of the
piezoelement 9 are formed on these surfaces. The piezoelement 9 is
secured on the housing 6 which also supports the stator winding 7, while
the rotor winding 8 is mounted on the axle 1. With the foregoing
arrangement, the axial play in the system is selected based on the
required axial and radial rigidity and should be from several to tens of
microns.

[0065] The electric motor illustrated in FIG. 1 operates as follows. An
excitation voltage is supplied by the generator 11. The excitation
voltage can be sinusoidal, at frequency νn0 corresponding to
the zero-order mode of "umbrella" oscillation of the saddle-resonators 4,
5. The excitation voltage is fed to the piezoelement 9 where, due to the
inverse piezoelectric effect, it produces a periodical in time
deformation "extension--contraction" corresponding to the d31 mode
of oscillation. The d31 mode of oscillation is well known in the art
and therefore will not be described here in detail. However, it should be
appreciated that with the d31 mode of oscillation, the vector of
primary radial oscillation of the piezoelement 9 is directed along the
planar end surface of attachment of the saddle-resonators 4, 5 and the
piezoelement 9, which causes periodic deformation of the piezoelement 9.
Due to the rigid connection between the piezoelement 9 and the
saddle-resonators 4, 5, this deformation is transferred to the
saddle-resonators 4, 5. Consequently, a standing wave with strong bending
deformation (due to the varying rigidity along the height of the
resonator ring) is established in the saddle-resonators 4, 5, which
causes "umbrella" type of oscillation. The standing wave causes the
conjugated surface of each saddle-resonator 4, 5 to develop micro-angular
oscillation. In particular, the conjugated surface of each
saddle-resonator 4, 5, owing to interaction with the gaseous medium,
commences to generate a directional acoustic field.

[0066] The directional acoustic field generated by each saddle-resonator
4, 5, is directed toward the conjugated surface of associated trunnion 2,
3, and toward its center of curvature of the conjugated surface. In other
words, each saddle-resonator 4, 5 becomes a source of an acoustic field.
This field is uniform and symmetrical over the entire surface of each
saddle-resonator 4, 5, due to the inherently high geometric stability and
symmetry of the support, the saddle-resonator surface manufacturing
quality, and the high Q factor of each saddle-resonator 4, 5 (it has been
established experimentally that Q=1,000-10,000). In this, the ultrasonic
wave shape is defined by the shape of the spherical surface of each
saddle-resonator 4, 5. The concave spherical surface of each
saddle-resonator 4, 5, forms a directional acoustic field shaped as a
spherical wave. While propagating in the gap between the conjugated
surfaces of the trunnions 2, 3, and the saddle-resonators 4, 5, the wave
is reflected by the similar convex surface of each trunnion 2, 3, and a
standing spherical acoustic wave is formed in the gap, i.e. the gap
begins functioning as a gaseous acoustic resonator. Consequently, the
spherical surface of each trunnion 2, 3 (like the spherical surface of
each saddle-resonator 4, 5) is acted upon by radiation acoustic pressure.

[0067] The axle system of this electric motor design in FIG. 1 is a
self-aligning one. The thickness of the actual working gap, which is the
same as the length of the acoustic resonator, is defined by compensation
of the forces developed by radiation acoustic pressure from the two
supports and the forces determined by the axial load-bearing capacity of
the motor. In this way, ultrasonic suspension of the rotor of the
electric motor is attained. A revolving magnetic field is formed at the
stator winding 7, which, in interaction with the rotor winding 8, applies
a rotary torque to the shaft of the electric motor.

[0068] As noted above, the piezoelement can be excited at frequency
νn0 corresponding to the zero-order mode of "umbrella"
oscillation of the saddle-resonator. As an alternative, the electric
motor in FIG. 1 can be excited with a voltage at frequency
νm0 formed at the output of the generator 11 such that the
excitation of the piezoelement is at the natural zero-order radial mode
of oscillation. However, if the natural zero-order radial mode of
oscillation is selected, the amplitude of oscillation in this mode should
be high enough to excite a corresponding flexural type of
saddle-resonator oscillation.

[0069] A resonant match takes place when the natural frequencies of the
zero order radial mode of oscillation of the piezoelement 9 and of the
zero order mode of "umbrella" vibration of the annular saddle-resonator
4, 5 coincide. When the system is designed this way, the excitation of
the vibrations in the annular saddle-resonators 4, 5 is the most
efficient. Note that if these two frequencies do not coincide, there are
two possible alternatives. A first alternative involves exciting the
piezoelement 9 on its natural frequency. Because the excitation profile
has a certain width, some of the energy on the wings of this excitation
profile will be transferred resonantly to the saddle resonators 4, 5. The
latter will be excited but the process will be inefficient. An
alternative is to excite the piezoelement 9 on the natural frequency of
the saddle-resonators 4, 5. In that case, the same result will occur for
the reasons described above. In either case, inefficient excitation will
result.

[0070] In the first embodiment of the electric motor shown in FIG. 1, the
natural frequencies of the saddle-resonators 4, 5 coincide, and therefore
they are excited from the common source of primary oscillation, namely
the piezoelement 9. While this approach has certain advantages, the
design also applies strict requirements to coincidence of the geometrical
parameters of the saddle-resonators 4, 5, their identical conjugation
with the piezoelement 9, and so forth. In some instances, these
requirements could be too restrictive, e.g. in minimization of the device
dimensions. Hence, a second embodiment of the electric motor with
independent excitation of each saddle-resonator 4, 5 is disclosed below.

[0071] Referring now to FIG. 2, there is shown a second embodiment of the
electric motor. The electric motor in FIG. 2 comprises an axle 1 on which
are centered and fixed the upper 2 and lower 3 spherical trunnions. The
trunnions 2, 3 contact along a similar spherical surface (shaped as a
spherical ring) with the respective upper 4 and lower 5 annular
saddle-resonators situated intermediate the trunnions 2 and 3.
Piezoelements 9, 10 are polarized normally to the planar end surfaces,
and electrodes of the piezoelements 9, 10 are formed on these surfaces.
The piezoelements 9, 10 are secured on the housing 6 which also supports
the stator winding 7, while the rotor winding 8 is mounted on the axle 1.
The axial play in the system amounts from several to tens of microns. In
this embodiment of the motor a second generator 12 is added for
excitation of the second piezoelement 10.

[0072] The electric motor illustrated in FIG. 2 operates as follows. Sine
wave excitation voltages are supplied by the two independent generators
11 and 12, at frequencies νn(4)0,νn(5)0
corresponding to the zero-order modes of the "umbrella" oscillations of
the saddle-resonators 4 and 5. The excitation voltages are fed,
respectively, to the piezoelements 9, 10 where, due to inverse
piezoelectric effect, oscillation mode d31 is induced in each
piezoelement 9, 10. In a d31 oscillation mode, the vector of primary
radial oscillation of each piezoelement 9, 10 is directed along the
planar end surface of the piezoelement 9, 10, which causes periodic
deformation of the piezoelement 9, 10. Due to the rigid connection
between the piezoelements 9, 10 and the associated saddle-resonators 4,
5, this deformation is transferred from each piezoelement 9, 10 to its
associated saddle-resonator 4, 5. Consequently, a standing wave with
strong bending deformation (due to the varying rigidity along the height
of the resonator ring) is established in the each of the
saddle-resonators 4, 5. The standing wave is responsible for the
ultrasonic suspension of the rotor.

[0073] As an alternative to a d31 oscillation mode, a radial
oscillation can be excited in the piezoelements 9, 10. In this case,
voltages at frequencies νm(9)0,νm(10)0 are
generated at the output of the two auxiliary independent generators 11,
12, and standing waves with strong bending deformations are established
in the saddle-resonators 4, 5, yielding ultrasonic suspension.

[0074] A third embodiment of the electric motor with internally-situated
trunnions 2, 3 is disclosed in FIG. 3. The internally-situated trunnions
2, 3 advantageously provide enhanced rigidity. This arrangement also
allows expanding the functionality of the electric motor. For instance,
when the spherical centers of the upper and lower trunnions 2, 3
coincide, a design of the electric motor with a floating shaft is
implemented. More particularly, in the design shown in FIG. 3 (and in
FIG. 6) the trunnion can slide (rock) on the cradle (when their spherical
centers coincide) simultaneously. With the remaining designs described
herein the rocking of the axis is restricted insofar as they allow only
rotational movement.

[0075] The third embodiment of the electric motor, FIG. 3, comprises an
axle 1 on which are centered and fixed the upper 2 and lower 3 spherical
trunnions. The trunnions 2, 3 are in close proximity to the respective
upper 4 and lower 5 annular saddle-resonators, along a spherical surface
(shaped as a spherical ring), with the trunnions 2, 3 situated between
the saddle-resonators 4, 5. The saddle-resonators 4, 5 are centered in a
similar manner with respect to the trunnions 2, 3, and are fixed on the
annular piezoelements 9, 10 along their planar end surfaces, with the
piezoelements 9, 10 situated above and under the associated
saddle-resonators 4, 5. The piezoelements 9, 10 are polarized normally to
the planar end surfaces, and the electrodes of the piezoelements 9, 10
are formed on these surfaces. The piezoelements 9, 10 are secured on the
housing 6 which also supports stator winding 7, while the rotor winding 8
is mounted on the axle 1. The axial play in the system amounts to several
to tens of microns.

[0076] The electric motor illustrated in FIG. 3 operates similarly to the
motor illustrated in FIGS. 1 and 2.

[0077] The first, second and third embodiments of the electric motor
utilize saddle-resonators that are fixed on the piezoelement 9, 10 along
a planar end surface. In each of these embodiments, the vector of primary
oscillation of the piezoelement 9, 10 is directed along this surface,
i.e. the d31 primary oscillation mode is excited in the piezoelement
9, 10. However, in some cases (for the sake of efficiency) it would be
advisable to design the bearing supports of the electric motor so that
the saddle-resonators 4, 5 are secured on the piezoelements 9, 10 along a
cylindrical surface, and the vector of primary oscillation of the
piezoelement 9, 10 would be directed normally to this surface. Therefore,
the fourth, fifth and sixth embodiments of the electric motor discussed
below in relation to FIGS. 4, 5 and 6, have this particular design of the
bearing supports.

[0078] Referring now to FIG. 4, a fourth embodiment of the electric motor
is disclosed. The electric motor in FIG. 4 comprises axle 1 on which are
centered and fixed the upper 2 and lower 3 spherical trunnions 2, 3. The
trunnions 2, 3 are in close proximity, along spherical surfaces (shaped
as a spherical rings), with the respective upper 4 and lower 5 annular
saddle-resonators situated intermediate the trunnions. The
saddle-resonators 4, 5 are similarly centered with respect to the
trunnions 2, 3, and are mounted on the annular piezoelement 9 so that
their cylindrical surfaces are secured to the inner cylindrical surface
of the piezoelement 9. The piezoelement 9 is polarized normally to the
planar end surfaces, i.e. radially, and electrodes of the piezoelement
are formed on the inner and outer radial surfaces as shown in FIG. 4. The
piezoelement 9 is secured on the housing 6 which also supports stator
winding 7, while the rotor winding 8 is mounted on the axle 1. The axial
play in the system amounts from several to tens of microns. The
piezoelement 9 is connected to the generator 11.

[0079] The electric motor illustrated in FIG. 4 operates similarly to the
motor illustrated in FIG. 1, except that the vector of primary
oscillation of the piezoelement 9 is directed normally to the cylindrical
surface of the saddle-resonators 4, 5, and that a d33 primary mode
of oscillation is excited in the piezoelement 9. This results in the
formation of "umbrella" oscillation, which has a greater amplitude of
excitation at both, frequency νn0 and at frequency
νm0, as compared to the embodiment of the electric motor
illustrated in FIG. 1. In this regard it will be appreciated that the
motor in FIG. 4 has a similar design to the motor in FIG. 1, but uses a
different excitation and polarization of the piezoelement 9 to achieve
greater amplitude of oscillation.

[0080] It is assumed in the fourth embodiment of the electric motor that
the natural frequencies of the saddle-resonator 4 and 5 are the same, so
that they are excited from the common source of primary oscillations--the
piezoelement 9. However, this arrangement may be difficult to implement
in some technologies, as has already been mentioned. Hence, a fifth
embodiment of the electric motor is suggested with independent excitation
of each saddle-resonator.

[0081] Referring now to FIG. 5, a fifth embodiment of the electric motor
is disclosed. The embodiment of the invention in FIG. 5 comprises an axle
1 on which are centered and fixed the upper 2 and lower 3 spherical
trunnions. The trunnions are in close proximity, along a similar
spherical surface (shaped as a spherical ring), with the respective upper
4 and lower 5 annular saddle-resonators situated intermediate the
trunnions 2, 3. The saddle-resonators 4, 5 are similarly centered with
respect to the trunnions 2,3, and are mounted on the upper 9 and lower 10
annular piezoelements so that their cylindrical surfaces are fast with
the inner cylindrical surface of the associated piezoelement 9, 10. The
piezoelements 9, 10 are polarized normally with respect to the
cylindrical surfaces, and electrodes of the piezoelements 9, 10 are
formed on these surfaces. The piezoelements 9, 10 are secured on the
housing 6 which also supports stator winding 7, while rotor winding 8 is
mounted on the axle. The axial play in the system amounts from several to
tens of microns.

[0082] The electric motor illustrated in FIG. 5 operates similarly to the
motor illustrated in FIG. 2, except the vector of primary oscillation of
the piezoelements 9, 10 is directed normally to the cylindrical surface
of the saddle, and a d33 primary mode of oscillation is excited in
the piezoelements 9, 10.

[0083] Similar to the third embodiment of the electric motor, the sixth
embodiment disclosed herein allows to enhance radial rigidity (over that
of the fourth and fifth embodiments) and to expand the functionality of
the motor. The sixth embodiment of the electric motor shown in FIG. 6,
comprises an axle 1 on which are centered and fixed the upper 2 and lower
3 spherical trunnions. The trunnions 2, 3 are in close proximity, along a
similar spherical surface (shaped as a spherical ring), with the
respective upper 4 and lower 5 annular saddle-resonators, with the
trunnions 2, 3 situated intermediate the saddle-resonators 4, 5. The
saddle-resonators 4, 5 are similarly centered with respect to the
trunnions 2, 3, and are mounted on the upper 9 and lower 10 annular
piezoelements so that their cylindrical surfaces are fast with the inner
cylindrical surface of the associated piezoelement 9, 10. The
piezoelements 9, 10 are polarized normally to their cylindrical surfaces,
and electrodes of the piezoelements 9, 10 are formed on these surfaces.
The piezoelements 9, 10 are secured on the housing 6 which also supports
stator winding 7, while rotor winding 8 is mounted on the axle 1. The
axial play in the system amounts from several to tens of microns. The
electric motor illustrated in FIG. 6 operates similarly to the motor of
the fifth embodiment illustrated in FIG. 5.

[0084] The implementation of the disclosed embodiments allows obtaining
electric motors based on ultrasonic non-contact bearings with technical
service life as long as tens of years, load-carrying capacity of 0.1 to
1.0 kg and shaft spatial stability of a few microns. The motors described
herein have numerous advantages including: virtual elimination of
vibration and noise in such motors, minimization of drag torque, the
absence of parasitic angular moments and the shaft self-centering
property (resulting in self-balancing) due to the nonlinear elasticity of
the bearing supports. Note that these properties allow the motors to
accelerate to high angular speeds (as high as tens of thousands of rpm)
and thus increase their usage and applicability to a higher,
qualitatively new level.